[R] Unable to run smoother in qplot() or ggplot() - complains about knots

[Christopher David Desjardins]

I get the following error when I run qplot()

qplot(grade, read,data = hhm.long.m, geom = c("point", "smooth"))

Error in smooth.construct.cr.smooth.spec(object, data, knots) :
  x has insufficient unique values to support 10 knots: reduce k.

I am not sure how to tackle this problem. When I take a subsample (<  
1000) than I am able to run that function but with my sample of ~   
40,000 qplot gives me that error. I have 6 grades.
Please cc me on reply.
Thanks!
  Chris